鈴木 昭彦¹, 石田 孝宣², 大内 憲明²

Akihiko SUZUKI¹, Takanori ISHIDA², Noriaki OHUCHI²

¹東北大学大学院医学系研究科先端画像・ナノ医科学寄付講座, ²東北大学大学院医学系研究科腫瘍外科

¹Advanced Breast Cancer Imaging, Graduate School of Medicine, Tohoku University, ²Surgical Oncology, Graduate School of Medicine, Tohoku University

キーワード :

Breast cancer incidence continues to increase worldwide. Asian women’s breasts are characterised by higher density than other ethnic groups, and the age-specific incidence of female breast cancer in Asia peaks at ages 40-49，whereas that in Western countries peaks at ages 60-70. Although MG is the only method that has evidence supporting mortality reduction from breast cancer, it is known that MG screening accuracy gets lower in association with higher breast densities and younger ages.
On the other hand, breast ultrasonography has been employed clinically for decades in Japan, and not only palpable breast cancers have been visualized, but also impalpable breast cancers in dense breasts. Some small clinical trial and observation studies have revealed the power of supplemental US with MG in dense breasts, however, the evidence was remain low level. The Japan Strategic Anticancer Randomized Trial（J-START）is the first large-scale RCT to verify the quality and effectiveness of US for breast cancer screening in women aged 40-49 years, with 76,196 participants had been enrolled by the end of fiscal year of 2012（March 31，2013）.
Of 76,196 women enrolled, 36,859 were assigned to the intervention group and 36,139 to the control group. Sensitivity was significantly higher in the intervention group than in the control group（91.1％，95％CI 87.2-95.0 vs 77.0％，70.3-83.7; p=0.0004）, whereas specificity was significantly lower（87.7％，87.3-88.0 vs 91.4％，91.1-91.7; p＜0.0001）. More cancers were detected in the intervention group than in the control group（184［0.50％］vs 117［0.32％］，p=0.0003）and were more frequently stage 0 and I（144［71.3％］vs 79［52.0％］，p=0.0194）．18（0.05％）interval cancers were detected in the intervention group compared with 35（0.10％）in the control group（p=0.034）.
Ultrasonography could offer a lowcost way to increase sensitivity and detection rates of early cancers in women with dense breasts, however, there are many problems to be overcome to recreate the excellent result of clinical trial in daily clinical medicine. Education system for screener and physician must be established, and quality assessment manual for the equipment also must be established in order to maintain the total quality of US screening. Minimising screening associated harms, such as high recall rate and low specificity, is very important. We must reinvestigate the validity of categorisation in screening, verify the overdiagnosis, and keep examining how the mortality changed.